3000 feet is just a general guideline for the altitude that the topography of the park starts making natural barriers. There are lots of natural barriers well below that mark that hold brook trout above them.

I was kind of hoping someone would just come along and elaborate on a few more of these locations... obviously I'm new and so my list is fairly short. Any recommendations?

Your comments about the valley seem to make sense as well... less bows and browns, less competition, hence more brooks moving/surviving downstream than in the past?